Stressed Seedlings Research Articles

Phlorotannins contribute to the ameliorative bioactivities of Ecklonia maxima-derived bioproduct in salt-stressed Solanumlycopersicum

Seaweed-derived bioproducts are increasingly being deployed as an environmentally friendly and sustainable approach to crop management under stressful growth conditions including salinity. The bioactivities of seaweed-derived extracts are linked to the presence of diverse groups of bioactive compounds. In the present study, the phlorotannins present in the seaweed Ecklonia maxima and Kelpak®, an E. maxima-derived bioproduct, were quantified and identified. Three phlorotannins were identified in E. maxima, namely eckol, 2-phloroeckol, and dibenzodioxin-fucodiphloroethol. Eckol (589.11 – 822.54 μg l−1) and dibenzodioxin-fucodiphloroethol (85 – 895 μg l−1) were present in Kelpak®. Phlorotannin bioactivity was investigated in tomato seedlings grown under NaCl-induced salinity stress. The seedlings treated with either individual phlorotannins (i.e., eckol or a fraction containing 2-phloroeckol and dibenzodioxin-fucodiphloroethol) or Kelpak® resulted in a reprogramming of biomass allocation as indicated by an increased root-to-shoot ratio. Phlorotannin and Kelpak® treatments induced the accumulation of antioxidants with an attendant augmentation of the antioxidant capacities and inhibition of membrane damage in the NaCl-stressed seedlings. Kelpak® treatment induced an increase in abscisic acid (ABA) accumulation and phlorotannin treatments lowered the ABA content of the stressed seedlings. These results demonstrated that phlorotannins contributed to the ameliorative actions of Kelpak®. The more potent effects of Kelpak®, in comparison to phlorotannins, in improving dry matter accumulation, ABA content, antioxidative properties, and inhibiting tissue injury of the salt-stressed tomato seedlings may be attributed to the presence of other bioactive components in the Kelpak® product.

Protective Role of Polyethylene Glycol Towards the Damaging Effects of Cadmium.

This study aimed to evaluate the role of drought-induced changes in the effects of cadmium (Cd) in plants. Cd is the most hazardous and important environmental pollutant. Water deficit is the most common environmental stress encountered by plants and affects most of the plant functions. The present study assessed the effect of Cd and water deficit on Capsicum frutescens seedlings in single and combined treatments. The seedlings of Capsicum were grown in a hydroponic solution and treated with Cd. The seedlings were subjected to water deficit with the help of polyethylene glycol (PEG). The other set of seedlings was treated with combined Cd + PEG. In the absence of PEG, maximum Cd accumulation was observed. The root and shoot growth of the seedlings were affected under all treatments with maximum inhibition in Cd. Pigment, protein and sugar contents and nitrate reductase activity decreased significantly in all treatments, while proline content increased. Induction of oxidative damage occurred through the formation of free radicals which caused alteration in electrolyte leakage, lipid peroxidation and activities of antioxidant enzymes, viz. superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase and non-enzymatic non-protein thiol content and ascorbic acid in the stressed seedlings. Water deficit buttressed the toxic effect of Cd on chilli seedlings.

Enhancing drought stress tolerance and growth promotion in chiltepin pepper (Capsicum annuum var. glabriusculum) through native Bacillus spp.

The drought can cause a decrease in food production and loss of biodiversity. In northern Mexico, an arid region, the chiltepin grows as a semi-domesticated crop that has been affected in its productivity and yield. An alternative to mitigate the effect of drought and aid in its conservation could be using Plant Growth-Promoting Bacteria (PGPB). The present study evaluated the capacity of native Bacillus spp., isolated from arid soils, as PGPBs and drought stress tolerance inducers in chiltepin under controlled conditions. Chiltepin seeds and seedlings were inoculated with native strains of Bacillus spp. isolated from arid soils, evaluating germination, vegetative, and drought stress tolerance parameters. The PGPBs improved vegetative parameters such as height, stem diameter, root length, and slenderness index in vitro. B. cereus (Bc25-7) improved in vitro survival of stressed seedlings by 68% at −1.02 MPa. Under greenhouse conditions, seedlings treated with PGPBs exhibited increases in root length (9.6%), stem diameter (13.68%), leaf fresh weight (69.87%), and chlorophyll content (38.15%). Bc25-7 alleviated severe water stress symptoms (7 days of water retention stress), and isolates B. thuringiensis (Bt24-4) and B. cereus (Bc25-7, and Bc30-2) increased Relative Water Content (RWC) by 51%. Additionally, the treated seeds showed improved germination parameters with a 46.42% increase in Germination Rate (GR). These findings suggest that using PGPBs could be an alternative to mitigate the effect of drought on chiltepin.

Exogenously applied putrescine regulates aluminium [al (III)] stress in maize (Zea mays L.): Physiological and metabolic implications

In this study, we investigated the role of exogenous application of putrescine (Put) for alleviation of Al (III) stress responses in maize seedlings. In presence of Put, the growth and biomass improved substantially in Al (III) stressed seedlings as compared to Al (III) alone. The production of hydrogen peroxide (H2O2) and superoxide radical (O2•-) were significantly restrained in during Al (III) stress in Put supplemented seedlings. The malondialdehyde (MDA) production was significantly controlled during Al (III) stress by Put supplementation as compared to the seedlings under Al (III) stress alone. The histochemical analysis showed variation in staining intensities of diaminobenzidine (DAB) and nitoroblue tetrazolium (NBT) salt to detect the presence of H2O2 and O2•- respectively, reflected strong role of Put in regulation of reactive oxygen species (ROS) production. The staining of roots with Schiff's reagent and Evans blue dye to detect lipid peroxidation and loss of plasma membrane integrity showed that Put controls the lipid peroxidation and maintains the integrity of the plasma membrane during Al (III) stress. The proton (1H) nuclear magnetic resonance (NMR) analysis of methanolic extracts of root and shoot of maize seedlings under Al (III) stress in presence or absence of Put showed considerable disparity in terms of metabolic profiles, which include amino acids, sugars, carbohydrates, organic acids and several aliphatic and aromatic compounds. The present study exhibited the potential role of Put for mitigation of Al (III) stress by enhancing growth, regulating ROS production, reducing oxidative stress, improving antioxidant metabolism and maintaining the metabolic pool.

Nitric oxide acts upstream of indole-3-acetic acid in ameliorating arsenate stress in tomato seedlings

After their discovery, nitric oxide (NO) and indole-3-acetic acid (IAA) have been reported as game-changing cellular messengers for reducing abiotic stresses in plants. But, information regarding their shared signaling in regulating metal stress is still unclear. Herein, we have investigated about the joint role of NO and IAA in mitigation of arsenate [As(V)] toxicity in tomato seedlings. Arsenate being a toxic metalloid increases the NPQ level and cell death while decreasing the biomass accumulation, photosynthetic pigments, chlorophyll a fluorescence, endogenous NO content in tomato seedlings. However, application of IAA or SNP to the As(V) stressed seedlings improved growth together with less accumulation of arsenic and thus, preventing cell death. Interestingly, addition of c-PTIO, {2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide, a scavenger of NO} and 2, 3, 5-triidobenzoic acid (TIBA, an inhibitor of polar auxin transport) further increased cell death and inhibited activity of GST, leading to As(V) toxicity. However, addition of IAA to SNP and TIBA treated seedlings reversed the effect of TIBA resulting into decreased As(V) toxicity. These findings demonstrate that IAA plays a crucial and advantageous function in NO-mediated reduction of As(V) toxicity in seedlings of tomato. Overall, this study concluded that IAA might be acting as a downstream signal for NO-mediated reduction of As(V) toxicity in tomato seedlings.

Bacillus licheniformis Jrh14-10 enhances alkaline tolerance in Arabidopsis thaliana by regulating crosstalk between ethylene and polyamine pathways.

Plant growth-promoting rhizobacteria (PGPR) are known for their role in ameliorating plant stress, including alkaline stress, yet the mechanisms involved are not fully understood. This study investigates the impact of various inoculum doses of Bacillus licheniformis Jrh14-10 on Arabidopsis growth under alkaline stress and explores the underlying mechanisms of tolerance enhancement. We found that all tested doses improved the growth of NaHCO3-treated seedlings, with 109 cfu/mL being the most effective. Transcriptome analysis indicated downregulation of ethylene-related genes and an upregulation of polyamine biosynthesis genes following Jrh14-10 treatment under alkaline conditions. Further qRT-PCR analysis confirmed the suppression of ethylene biosynthesis and signaling genes, alongside the activation of polyamine biosynthesis genes in NaHCO3-stressed seedlings treated with Jrh14-10. Genetic analysis showed that ethylene signaling-deficient mutants (etr1-3 and ein3-1) exhibited greater tolerance to NaHCO3 than the wild type, and the growth-promoting effect of Jrh14-10 was significantly diminished in these mutants. Additionally, Jrh14-10 was found unable to produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, indicating it does not reduce the ethylene precursor ACC in Arabidopsis. However, Jrh14-10 treatment increased the levels of polyamines (putrescine, spermidine, and spermine) in stressed seedlings, with spermidine particularly effective in reducing H2O2 levels and enhancing Fv/Fm under NaHCO3 stress. These findings reveal a novel mechanism of PGPR-induced alkaline tolerance, highlighting the crosstalk between ethylene and polyamine pathways, and suggest a strategic redirection of S-adenosylmethionine towards polyamine biosynthesis to combat alkaline stress.

Zinc and copper toxicity in basil (Ocimum basilicum L.) seedlings: Role of melatonin in mitigating stress

The effects of melatonin (MT) on the growth and antioxidant responses of basil (Ocimum basilicum L.) exposed to copper and zinc excess stress are investigated. For this purpose, seedlings were exposed to different concentrations of copper oxide (0, 50 and 150 µM), zinc oxide (0, 50 and 100 µM) and melatonin (0 and 100 µM) for 14 days. Growth and biochemical parameters, the activity of some antioxidant enzymes, and phenylalanine ammonia lyase (PAL) and some of the main nutritional elements in the shoot and root of seedlings were measured. The results of this study showed that the excess of copper (Cu 50 and 150 µM) and zinc (Zn 50 and 100 µM) causes a decrease in growth, and a higher oxidative stress indicator such as hydrogen peroxide and malondialdehyde (MDA) content. The homeostasis balance of mineral nutrition of basil seedlings was also disrupted under copper and zinc stress. Melatonin treatment in Cu, Zn stressed seedlings improved growth parameters by reducing the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and increasing the activity of PAL and antioxidant enzymes. Melatonin also regulated the distribution of minerals in basil seedlings under Cu and Zn stress conditions. The results of this research showed that MT can improve the tolerance of basil seedlings against copper and zinc stress by modulate growth and antioxidant responses and regulating mineral nutrition.

Screening of Eucalyptus camaldulensis clones for enhancing productivity and sustainability in problematic soils of Southern India

Among the various challenges faced by eucalyptus plantations in the Indian pulp industry, one of them is the development of resilient clones adaptable to saline soils. Large genetic diversity exists in E. camaldulensis because of high out-crossing rates and is expected to pass traits into the new developed clones. We used a salt injury score, survival percentage and proline content as a screening criterion to select new clones tolerant to high salt levels in soils. Proline has been identified as a beneficial solute in plants under stress caused by high salinity. Three months old clones of eleven new eucalyptus genotypes were transplanted in pots with free-draining coarse river sand. Four treatments comprising control, high Salt, High Salt + High pH and High pH were arranged in a randomised block design. Common salt (NaCl) was used for regulating salt concentrations while sodium bicarbonate (NaHCO3) was used for regulating the pH of the solutions. NaCl concentrations were increased every third day until the final concentration of 150 mM was reached. Similarly, pH of the solutions was also gradually increased till final pH of 10 was attained. Each treatment solution was delivered through automated drip delivery. Salt injury scores based on symptoms were positively correlated (0.812) with survival percentage and proline content. Eucalyptus genotypes were classified into five salt tolerant groups: tolerant (T), moderately tolerant (MT), moderately sensitive (MS), sensitive (S), and highly sensitive (HS). The mean values of proline content in leaves were different among the five groups, indicating that the proline content is a reliable marker for identifying salt tolerance. Proline contents in stressed seedlings were significantly different between the tolerant and highly sensitive groups, but the difference among the intermediate groups (MT, MS and S) was not significant. As the stress levels of salt and pH were increased, the sensitive hybrid clone tested showed very poor growth, which was also negatively correlated with the proline content in its leaves. Combination of high salt and high pH was also found to be correlated with reduced proline content, poor growth and survival among sensitive genotypes. In addition to the commonly used sodium and pH induced symptoms, proline content is suggested to be another useful criterion to differentiate salt-tolerant from salt-sensitive genotypes. This study helped in classification of genotypes with different levels of salt and pH tolerance, which may be used for deployment of genotypes according to changing edaphic conditions for sustainability of eucalyptus plantations.

Methyl jasmonate reduces cadmium toxicity by enhancing phenol and flavonoid metabolism and activating the antioxidant defense system in pigeon pea (Cajanus cajan)

Cadmium (Cd) is absorbed by plant roots from soil along with essential nutrients and affects plant growth and productivity. Methyl jasmonate (Me-JA) play important roles to mitigate Cd toxicity in plants. We have investigated the role of Me-JA to ameliorate Cd toxicity in Pigeon pea (Cajanus cajan). Plant root growth, biomass, cellular antioxidant defense system and expression of key regulatory genes in molecular and signaling process have been analyzed. Two Cajanus cajan varieties AL-882 and PAU-881 were grown at 25 °C, 16/8h light/dark conditions in three biological replicates at 5 mM Cd concentration, three concentration of Me-JA (0, 10 nM, 100 nM) and two concentrations in combination of Me-JA + Cd (10 nM Me-JA +5 mM Cd, 100 nM Me-JA +5 mM Cd). The seedlings were exposed to Cd stress consequently plants showed decrease in primary root growth (60.71%, in AL-882 and 8.33%, in PAU-881), shoot and root biomass and antioxidant enzymes activities. Me-JA treatment resulted in increased primary root growth (63.64%, in AL-882) and overall plant biomass. Oxidative stress generated due to Cd stress was counter balanced by Me-JA treatment. Me-JA reduced H2O2 free radicals formation and enhanced antioxidant enzyme activities and phenolic content in stressed seedlings. Me-JA treatment increased expression of CALM, IP3, CDPK2, MPKs (involved in calcium and kinase signaling pathways) and reduced expression of metal transporters (IRT1 and HMA3) genes. This reduction in metal transporters gene expression is a probable reason for low toxicity effect of Cd in root after Me-JA treatment which has potential implications in reducing the risk of Cd in the food chain.

Titanium dioxide nanoparticles require K+ and hydrogen sulfide to regulate nitrogen and carbohydrate metabolism during adaptive response to drought and nickel stress in cucumber

Crop plants face severe yield losses worldwide owing to their exposure to multiple abiotic stresses. The study described here, was conducted to comprehend the response of cucumber seedlings to drought (induced by 15% w/v polyethylene glycol 8000; PEG) and nickel (Ni) stress in presence or absence of titanium dioxide nanoparticle (nTiO2). In addition, it was also investigated how nitrogen (N) and carbohydrate metabolism, as well as the defense system, are affected by endogenous potassium (K+) and hydrogen sulfide (H2S). Cucumber seedlings were subjected to Ni stress and drought, which led to oxidative stress and triggered the defense system. Under the stress, N and carbohydrate metabolism were differentially affected. Supplementation of the stressed seedlings with nTiO2 (15 mg L−1) enhanced the activity of antioxidant enzymes, ascorbate-glutathione (AsA-GSH) system and elevated N and carbohydrates metabolism. Application of nTiO2 also enhanced the accumulation of phytochelatins and activity of the enzymes of glyoxalase system that provided additional protection against the metal and toxic methylglyoxal. Osmotic stress brought on by PEG and Ni, was countered by the increase of proline and carbohydrates levels, which helped the seedlings keep their optimal level of hydration. Application nTiO2 improved the biosynthesis of H2S and K+ retention through regulating Cys biosynthesis and H+-ATPase activity, respectively. Observed outcomes lead to the conclusion that nTiO2 maintains redox homeostasis, and normal functioning of N and carbohydrates metabolism that resulted in the protection of cucumber seedlings against drought and Ni stress. Use of 20 mM tetraethylammonium chloride (K+- channel blocker), 500 μM sodium orthovanadate (PM H+-ATPase inhibitor), and 1 mM hypotaurine (H2S scavenger) demonstrate that endogenous K+ and H2S were crucial for the nTiO2-induced modulation of plants' adaptive responses to the imposed stress.

Monitoring Role of Exogenous Amino Acids on the Proteinogenic and Ionic Responses of Lettuce Plants under Salinity Stress Conditions

Lettuce plants (Lactuca sativa L.) were grown under salinity stress conditions. Amino acids (histidine (His), lysine (Lys), phenylalanine (Phe), and threonine (Thr)) were individually applied to the seedlings to study their impact on the status of the photosynthetic pigments, ion absorption, proteinogenic metabolism, and peroxidase activity. Investigating the effect of exogenous amino acids on the metabolism processes showed their potential role in inducing salt stress tolerance in lettuce plants. Generally, a destructive impact on lettuce plant morphology was observed when the plants were exposed to salt stress. In contrast, the significant (p < 0.05) mitigation of salt stress was registered when EAAs were applied to the stressed seedlings while using Threonine and lysine enhanced the status of the plants under salinity stress. For the salt treatment, the maximum electric conductivity (580.2 μS/g) was reported while applying EAAs to stressed plants’ decreased EC, and the data ranged from 522 to 554 μS/g. EAAs decreased the chloride ions in the leaves by 23–30% compared to in the stressed plants. Additionally, the sodium contents were mitigated when the stressed plants were sprayed with EAAs. In contrast, applying EAAs enhanced the potassium uptake, and Thr gave the highest K+ contents (3022 μg/g). EAAs increased the chlorophyll content compared to the control except when histidine was applied, while the carotene contents significantly increased when histidine and phenylalanine were used. Endogenous amino acids are highly expressed in non-stressed lettuce plants compared to the stressed ones. Under salt stress conditions, the threonine usage increased the expression of proteinogenic amino acids except methionine and tyrosine. Compared to the salt-stressed plants, the peroxidase activity significantly decreased in the other treatments, which fell by over 32% when His, Lys, and Phe were applied.

Gibberellic Acid Supplements Mitigate the Sodium Chloride Effects on Onion Seed Germination and Its Physio-Chemical Attributes

The mitigative effect of gibberellic acid (GA3) for salt (NaCl) stresses on seed germination attributes of onion (Allium cepa L.) cultivar Nasarpuri was assessed. Seeds were moisturized with NaCl (0-, 100- and 200-mM) and GA3 (250 ppm) before and after sowing for seed germination in 1st week than in 2nd week, GA3 sprayed once foliarly and NaCl in rooting region. At the end of 1st week, an increase in seed germination rate was observed in seeds supplemented with GA3 from control (85.0%) to 97.5% and from NaCl stressed seeds (72.5% and 50.0%) to 85.0% and 62.5%, respectively (p ≤ 0.05). This reduction in seed germination was caused by salt stresses after 96th hours of sowing, inhibition in GA3-biosynthesis GA3 and delay in α-amylases activation observed in salt stressed seed cultures. The seedling vigor index (SVI) was observed higher in foliarly GA3 sprayed cultures of both control as well as saline stressed cultures. The seedlings supplemented with GA3, decrease in malondialdehyde (MDA), H2O2, Na+/K+, Na+ and Cl- contents, while increases seedling biomass, chlorophyll contents, total proteins, and sugars in NaCl stressed seedlings. Interestingly, GA3 also increased (p ≤ 0.05) the osmoprotectants in seedlings including abscisic acid (AsA), carotenoids, phenolics and proline contents to depict in stress alleviation. This study may be concluded by the fact that GA3 minimizes salinity stresses on seed germination as well as further seedling growth with the increased production of organic osmoprotectants as saline stress neutralizers.

Climate Change, Megafires Crush Forest Regeneration

High-intensity fires in western states kill mature trees and their seeds while warmer, drier conditions stress seedlings. But forest managers can still intervene to change this trajectory.

Melatonin involves hydrogen sulfide in the regulation of H+-ATPase activity, nitrogen metabolism, and ascorbate-glutathione system under chromium toxicity

Contamination of soils with chromium (Cr) jeopardized agriculture production globally. The current study was planned with the aim to better comprehend how melatonin (Mel) and hydrogen sulfide (H2S) regulate antioxidant defense system, potassium (K) homeostasis, and nitrogen (N) metabolism in tomato seedlings under Cr toxicity. The data reveal that application of 30 μM Mel to the seedlings treated with 25 μM Cr has a positive effect on H2S metabolism that resulted in a considerable increase in H2S. Exogenous Mel improved phytochelatins content and H+-ATPase activity with an associated increase in K content as well. Use of tetraethylammonium chloride (K+-channel blocker) and sodium orthovanadate (H+-ATPase inhibitor) showed that Mel maintained K homeostasis through regulating H+-ATPase activity under Cr toxicity. Supplementation of the stressed seedlings with Mel substantially scavenged excess reactive oxygen species (ROS) that maintained ROS homeostasis. Reduced electrolyte leakage and lipid peroxidation were additional signs of Mel's ROS scavenging effects. In addition, Mel also maintained normal functioning of nitrogen (N) metabolism and ascorbate-glutathione (AsA-GSH) system. Improved level of N fulfilled its requirement for various enzymes that have induced resilience during Cr stress. Additionally, the AsA-GSH cycle's proper operation maintained redox equilibrium, which is necessary for the biological system to function normally. Conversely, 1 mM hypotaurine (H2S scavenger) abolished the Mel-effect and again Cr-induced impairment on the above-mentioned parameters was observed even in presence of Mel. Therefore, based on the observed findings, we concluded that Mel needs endogenous H2S to alleviate Cr-induced impairments in tomato seedlings.

Activated charcoal alleviates fluoride stress by restricting fluoride uptake and counteracting oxidative damages in the rice cultivar MTU1010

This work was aimed to explore the efficacy of activated charcoal (5 mg g-1 soil) in abating fluoride (25 mg L-1 NaF) stress in rice seedlings, since the protective role of charcoal is widely reported against other forms of abiotic stress. Application of NaF solution reduced germination rate, dry and fresh weight, and shoot and root length of seedlings. Extensive fluoride accumulation lowered the chlorophyll level along with higher electrolyte leakage and formation of H2 O2 , malondialdehyde, and methylglyoxal. Administration of activated charcoal lowered the extent of oxidative damages by inhibiting the uptake of fluoride ions. Exogenous application of activated charcoal also restored the activity of Kreb's cycle enzymes, i.e. PDH, IDH, MDH, and SDH, thereby overcoming the burden of carbon utilization and energy depletion occurring during stress. Additionally, the osmolyte (soluble sugar, proline, glycine-betaine, and amino acid) level was further escalated in presence of activated charcoal. The inhibition in catalase activity in fluoride-stressed seedlings was also restored. The activity of a range of enzymatic antioxidants (guaiacol peroxidase, superoxide dismutase, and ascorbate peroxidase) along with the glyoxalase system associated-enzymes (glyoxalase I and II) was further triggered in stressed seedlings treated with activated charcoal. The enhanced level of carotenoids, ascorbic acid, and total phenolics also enabled efficient scavenging of reactive oxygen species, thereby reducing cellular necrosis in the leaves. Based on the current investigation, it can be concluded that activated charcoal application appears a promising strategy to improve growth and mitigate damages in rice plants, growing in fluoride-polluted soil.

Physio-biochemical characterization of wheat genotypes under temperature stress.

Thermal stress is a major abiotic stress in wheat and ishighly complex in mechanism. A large area in northwestern plain zones (NWPZ), which is the wheat bowl of India is affected by heat stress. Climate change also causes anabrupt increase in temperature at different growth stages of wheat. Thus, wiser selection of stress tolerant varieties is an important strategy to combat the climate change effect. The present study aims for physiological and biochemical screening of timely sown NWPZ wheat varieties (WB2, HD3086, DBW88, DPW621-50, DBW17, HD2967 and PBW550) of India for their thermal stress tolerance along with heat tolerant (RAJ3765) and susceptible checks (RAJ4014) at seedling stage. The experiment was conducted in completely randomized design under controlled laboratory condition and heat stress was induced at 37°C at seedling stage. Later different physio-biochemical traits were studied in both control and stress seedlings. All traits exhibited significant variations among genotypes under heat stress condition. Root and shoot weight, relative water content, chlorophyll content index and chlorophyll fluorescence reduced significantly, whereas membrane leakage, osmotic potential, catalase, ascorbate peroxidase, guaiacol peroxidase, malondialdehyde content and proline content were increased in stress plants. A tolerance matrix was prepared based on stress response of the genotypes for each trait and a final tolerance score was given to each genotype. Based on this tolerance matrix, DBW88 and PBW550 were identified as tolerant, DPW621-50, DBW17 and HD2967 as moderately susceptible and HD3086 and WB2 as susceptible to heat stress. Earlier studies parade that seedling level stress tolerance has high correlation with adult level stress tolerance under field condition in wheat. Hence, this study helps in wiser selection of varieties for sowing in NWPZ based on weather forecast of the location for creating varietal mosaic in context of climate change.

Applied Selenium as a Powerful Antioxidant to Mitigate the Harmful Effects of Salinity Stress in Snap Bean Seedlings

Selenium (Se) plays several significant roles in regulating growth, development and plant responses to various abiotic stresses. However, its influence on sulfate transporters (SULTRS) and achieving the harmony with other salt-tolerance features is still limited in the previous literatures. This study elucidated the effect of Se supplementation (5, 10 and 20 µM) on salt-stressed (50 mM NaCl) snap bean seedlings. Generally, the results indicated that Se had dual effects on the salt stressed seedlings according to its concentration. At a low level (5 µM), plants demonstrated a significant improvement in shoot (13.8%) and root (22.8%) fresh weight, chlorophyll a (7.4%), chlorophyll b (14.7%), carotenoids (23.2%), leaf relative water content (RWC; 8.5%), proline (17.2%), total soluble sugars (34.3%), free amino acids (FAA; 18.4%), K (36.7%), Ca (33.4%), K/Na ratio (77.9%), superoxide dismutase (SOD; 18%), ascorbate peroxidase (APX;12.8%) and guaiacol peroxidase (G-POX; 27.1%) compared to the untreated plants. Meanwhile, most of these responses as well as sulfur (S), Se and catalase (CAT) were obviously decreased in parallel with increasing the applied Se up to 20 µM. The molecular study revealed that three membrane sulfate transporters (SULTR1, SULTR2 and SULTR 3) in the root and leaves and salinity responsive genes (SOS1, NHX1 and Osmotin) in leaves displayed different expression patterns under various Se treatments. Conclusively, Se at low doses can be beneficial in mitigating salinity-mediated damage and achieving the functioning homeostasis to tolerance features.

Exogenous melatonin induces tolerance to drought stress damage in seedlings and soybean plants

Melatonin (ML) is an indolamine that regulates a wide range of physiological processes as growth of roots and shoots, antioxidant enzyme activity, seed germination, photosynthetic efficiency promoting stress tolerance in plants, mitigating the harmful effects of abiotic stress. Effects of pretreatment of soybean (Glycine max (L.) Merr.) seeds with 10, 30, 60 and 90 μM ML were evaluated in seedlings under osmotic stress measuring germination speed index, and root protrusion, growth, and DM. Under osmotic stress, ML increased germination speed index at 10 (239%), 30 (194%) and 60 μM ML (189%); 5th-day root protrusion by 290%, 214%, 185% and 85% (10, 30, 60, and 90 μM ML respectively). The application of 10 (328%), 30 (224%), 60 (265%), 90 μM ML (129%) increased root length, followed by root DM in stressed seedlings. Drought stress reduced photosynthetic efficiency, increased ROS, and reduced antioxidant enzymatic activities in soybean. In a second experiment, well-watered (100% field capacity) (WW) and drought stressed (DS) soybean plants received 30 and 50 μM ML. Melatonin increased rate of CO2 assimilation and net photosynthetic rate at 30 μM ML (WW) in 28% (2 d after application) and 50 μM ML (DS) in 48% (5 d after application). Melatonin increased antioxidant enzymes activity (catalase and peroxidase) in plants under drought stress. The ML application enhanced leaf area in WW plants, however decreased in stressed plants. An increased number of seeds, pod numbers, total seed mass, root DM were observed under WW. Drought stress increased numbers of seeds (27%), pod numbers (33%) and total seeds mass (27%) with 30 μM ML. These results demonstrated that ML mitigated negative effects produced by drought on germination and growth of soybean seedlings, and acted as a drought tolerance inducer, improving yield under stress condition.

Interactive effect of 24-epibrassinolide and plant growth promoting rhizobacteria inoculation restores photosynthetic attributes in Brassica juncea L. under chlorpyrifos toxicity

Chlorpyrifos (CP) is a commonly used organophosphorous pesticide that is frequently utilised in the agricultural industry because of its great efficiency and inexpensive cost. The focus of the present study was to assess the impact of CP toxicity on Brassica juncea L. and to unravel the ameliorative potential of phytohormone, 24-epibrassinolide (EBL) mediated plant-microbe (Pseudomonas aeruginosa (B1), Burkholderia gladioli (B2)) interaction in B. juncea L. The maximum significant increment in the total chlorophyll, carotenoids, xanthophyll, anthocyanin and flavonoid content with EBL and B2 treatment in CP stressed B. juncea seedlings on spectrophotometric analysis were observed. Autofluorescence imaging of photosynthetic pigments i.e. chlorophyll, carotenoids, and total phenols with confocal microscopy showed maximum fluorescence with EBL and B2. Furthermore, when compared to CP stressed seedlings, scanning electron microscopy (SEM) study of the abaxial surface of leaves revealed a recovery in stomatal opening. The supplementation of EBL and PGPR (plant growth promoting rhizobacteria) improved the level of psb A (D1 subunit PSII) and psb B (CP 47 subunit of PSII) genes expression. The expression analysis of chalcone synthase (CHS), Phenylalanine ammonialyase (PAL), Phyotene synthase (PSY) with RT-PCR system showed up-regulation in the expression when supplemented with EBL and PGPR. As a result, the current study suggests that EBL and PGPR together, can reduce CP-induced toxicity in B. juncea seedlings and recovering the seedling biomass.

Alleviating effect of exogenous melatonin and calcium on the peroxidation damages of cucumber under high temperature stress

To explore whether there is an interaction between melatonin (MT) and calcium (Ca2+) in regulating heat tolerance of plants, we analyzed the response of endogenous MT and Ca2+ to heat stress, and examined the effect of MT and Ca2+ on the reactive oxygen (ROS) accumulation, antioxidant system, and transcripts of heat shock factor (HSF) and heat shock proteins (HSPs) of cucumber seedlings under high temperature stress. Seedlings were foliar sprayed with 100 μmol·L-1 MT, 10 mmol·L-1 CaCl2, 3 mmol·L-1 ethylene glycol tetraacetic acid (EGTA, Ca2+ chelating agent) +100 μmol·L-1 MT, 0.05 mmol·L-1 chlorpromazine (calmodulin antagonist, CPZ) +100 μmol·L-1 MT, 100 μmol·L-1 p-chlorophenylalanine (p-CPA, inhibitor of MT) +10 mmol·L-1 CaCl2 or deionized water (H2O), respectively. The results showed that both endogenous MT and Ca2+ in cucumber seedlings were induced by high temperature stress. The seedlings treated with exogenous MT showed significant increases in the mRNA expression of calmodulin (CaM), calcium-dependent protein kinase (CDPK5), calcineurin B-like protein (CBL3) and CBL interacting protein kinase (CIPK2) compared with the control at normal temperature. The mRNA levels of tryptophane decarboxylase (TDC), 5-hydroxytryptamine-N-acetyltransferase (SNAT) and N-acetyl-5-hydroxytryptamine methyltransferase (ASMT), key genes of MT biosynthesis and endogenous MT content were also induced by Ca2+ in cucumber seedlings. Exogenous MT and CaCl2 alleviated the heat-induced oxidative damage through increasing antioxidant ability, reducing the accumulation of reactive oxygen species (ROS), and upregulating the mRNA abundances of HSF7, HSP70.1 and HSP70.11, as evidenced by mild thermal damage symptoms, lower heat injury index and electrolyte leakage under heat stress. The positive effect of MT-induced antioxidant capacity and mRNA expression of HSPs was removed by adding EGTA and CPZ in stressed seedlings. Similarly, the mitigating role of Ca2+ in the peroxidation damage to high temperature stress was reversed by p-CPA. These results suggested that both MT and Ca2+ could induce heat tolerance of cucumber seedlings, which had crosstalk in the process of heat stress signal transduction.